Chromosome studies to ascertain the prevalence of chromosome abnormalities or variations in the population were initiated in the Fall of 1969. The populations under study are: 1. All the institutionalized juvenile delinquents in the state of Maryland. These are in the age group of 8 to 18 and are located primarily in five institutions under the administration of the Department of Juvenile Services. This number is estimated to be 6,000 in three years. 2. Boys from general population. Presently all boys up to age 18 years enrolled in the comprehensive child care program of the Pediatrics Department of the Johns Hopkins Hospital are being studied. Other groups will be from public and private schools, day care centers and nurseries. This number is estimated to be 7,500. 3. All boys from the Edgemeade of Maryland, a private treatment center for emotionally and mentally disturbed boys. This number is estimated to be 500 in three years. Consent for chromosome study on boys is being asked of the parents/legal guardians in this study. Clinical delineation of 47,xyy males is being attempted by physical, anthropometric, dermatoglyphis, endocrine, psychologic and psychiatric investigations.